Rework relative date functions (#352)

* Rework relative date functions

tl/tt/rel_date.go

@@ -0,0 +1,140 @@
+package tt
+
+import (
+	"errors"
+	"time"
+)
+
+// Allow for time mocking
+type Clock interface {
+	Now() time.Time
+}
+
+// Real system clock
+type RealClock struct{}
+
+func (dc RealClock) Now() time.Time {
+	return time.Now().In(time.UTC)
+}
+
+// A mock clock with a fixed time
+type MockClock struct {
+	T time.Time
+}
+
+func (dc MockClock) Now() time.Time {
+	return dc.T
+}
+
+// RelativeDate gets a date reltive to the provided time; currentTime should have timezone set.
+func RelativeDate(currentTime time.Time, relativeDateLabel string) (time.Time, error) {
+	// Current date
+	clNow := currentTime
+	clDay := clNow.Day()
+	clYear := clNow.Year()
+	clMonth := clNow.Month()
+	clHour := clNow.Hour()
+	clMin := clNow.Minute()
+	clSec := clNow.Second()
+	clLoc := clNow.Location()
+
+	// Parse date or use special label
+	dowOffset := -1
+	nextFlag := false
+	switch relativeDateLabel {
+	case "now":
+		// default
+	case "":
+		// equiv to "now"
+	case "sunday":
+		dowOffset = 0
+	case "monday":
+		dowOffset = 1
+	case "tuesday":
+		dowOffset = 2
+	case "wednesday":
+		dowOffset = 3
+	case "thursday":
+		dowOffset = 4
+	case "friday":
+		dowOffset = 5
+	case "saturday":
+		dowOffset = 6
+	case "next-sunday":
+		dowOffset = 0
+		nextFlag = true
+	case "next-monday":
+		dowOffset = 1
+		nextFlag = true
+	case "next-tuesday":
+		dowOffset = 2
+		nextFlag = true
+	case "next-wednesday":
+		dowOffset = 3
+		nextFlag = true
+	case "next-thursday":
+		dowOffset = 4
+		nextFlag = true
+	case "next-friday":
+		dowOffset = 5
+		nextFlag = true
+	case "next-saturday":
+		dowOffset = 6
+		nextFlag = true
+	default:
+		// Update to parsed YYYY-MM-DD
+		t, err := time.Parse("2006-01-02", relativeDateLabel)
+		if err != nil {
+			return time.Time{}, errors.New("could not parse date")
+		}
+		clYear = t.Year()
+		clMonth = t.Month()
+		clDay = t.Day()
+	}
+
+	// Construct time from parsed components
+	baseTime := time.Date(clYear, clMonth, clDay, clHour, clMin, clSec, 0, clLoc)
+
+	// Check the next 7 days to get the correct weekday
+	if dowOffset >= 0 {
+		i := 0
+		if nextFlag {
+			i = 1
+		}
+		for ; i < 8; i++ {
+			dowTime := baseTime.AddDate(0, 0, i)
+			curDow := dowTime.Weekday()
+			if int(curDow) == dowOffset {
+				// Update and
+				return dowTime, nil
+			}
+		}
+	}
+	return baseTime, nil
+}
+
+// FallbackDate gets an equivalent day-of-week within fallbackWeek if currentTime is not with startTime/endTime bounds
+func FallbackDate(currentTime time.Time, startTime time.Time, endTime time.Time, fallbackWeek time.Time) (time.Time, bool, error) {
+	loc := currentTime.Location()
+	startTime = midnight(startTime, loc)
+	endTime = midnight(endTime, loc).AddDate(0, 0, 1)
+	if endTime.Before(startTime) {
+		return currentTime, false, errors.New("end time before start time")
+	}
+	if currentTime.Before(startTime) || currentTime.After(endTime) {
+		// fmt.Println("using fallback: ", fallbackTime, "date:", baseTime, "bounds:", startTime, endTime)
+		ft := midnight(fallbackWeek, currentTime.Location())
+		for i := 0; i < 7; i++ {
+			if ft.Weekday() == currentTime.Weekday() {
+				currentTime = time.Date(ft.Year(), ft.Month(), ft.Day(), currentTime.Hour(), currentTime.Minute(), currentTime.Second(), 0, loc)
+				return currentTime, true, nil
+			}
+			ft = ft.AddDate(0, 0, 1)
+		}
+	}
+	return currentTime, false, nil
+}
+
+func midnight(t time.Time, loc *time.Location) time.Time {
+	return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, loc)
+}